U.S. Pat. No. 5,985,848, U.S. Pat. No. 6,066,722 and U.S. Pat. No. 6,228,741 are directed to nucleoside analogues that are inhibitors of purine nucleoside phosphorylase (PNP) and purine phosphoribosyltransferases (PPRT). The analogues are useful in treating parasitic infections, T-cell malignancies, autoimmune diseases and inflammatory disorders. The analogues are also useful for immunosuppression in organ transplantation.
PCT/NZ00/00048 provides a process for preparing certain PNP inhibitor compounds. This application recognises the compounds as PNP inhibitors and addresses a need for simpler methods of preparing them. PCT/NZ01/00174 also provides further nucleoside analogues that are inhibitors of PNP and PPRT.
Certain nucleoside analogues have also been identified as potent inhibitors of 5′-methylthioadenosine phosphorylase (MTAP) and 5′-methylthioadenosine nucleosidase (MTAN). These are the subject of PCT/NZ03/00050.
The applicants of the present application have also developed a process for preparing methylene linked cyclic amine deazapurines including reacting formaldehyde, or a formaldehyde equivalent, with a cyclic amine and a heteroaromatic compound. This process is the subject of New Zealand patent application no. 523970
PNP catalyses the phosphorolytic cleavage of ribo- and deoxyribonucleosides, for example those of guanine and hypoxanthine, to give the corresponding sugar-1-phosphate and guanine, hypoxanthine or other purine bases.
Humans deficient in purine nucleoside phosphorylase (PNP) suffer a specific T-cell immunodeficiency due to an accumulation of dGTP which prevents proliferation of stimulated T lymphocytes. Inhibitors against PNP are therefore immunosuppressive, and are active against T-cell malignancies and T-cell proliferative disorders.
Nucleoside hydrolases (NH) catalyse the hydrolysis of nucleosides. These enzymes are not found in mammals but are required for nucleoside salvage in some protozoan parasites. Some protozoan parasites use nucleoside phosphorylases either instead of or in addition to, nucleoside hydrolases for this purpose. Inhibitors of nucleoside hydrolases and phosphorylases can be expected to interfere with the metabolism of the parasite and can therefore be usefully employed against protozoan parasites.
MTAP and MTAN function in the polyamine biosynthesis pathway, in purine salvage in mammals, and in the quorum sensing pathways in bacteria. MTAP catalyses the reversible phosphorolysis of 5′-methylthioadenosine (MTA) to adenine and 5-methylthio-α-D-ribose-1-phosphate (MTR-1P). MTAN catalyses the reversible hydrolysis of MTA to adenine and 5-methylthio-α-D-ribose and of S-adenosyl-L-homocysteine (SAH) to adenine and S-ribosyl-homocysteine (SRH). The adenine formed is subsequently recycled and converted into nucleotides. Essentially, the only source of free adenine in the human cell is a result of the action of these enzymes. The MTR-1P is subsequently converted into methionine by successive enzymatic actions.
MTA is a by-product of the reaction involving the transfer of an aminopropyl group from decarboxylated S-adenosylmethionine to putrescine during the formation of spermidine. The reaction is catalyzed by spermidine synthase. The spermidine synthase is very sensitive to product inhibition by accumulation of MTA. Therefore, inhibition of MTAP or MTAN severely limits the polyamine biosynthesis and the salvage pathway for adenine in the cells. Likewise, MTA is the by-product of the bacterial synthesis of acylated homoserine lactones from S-adenosylmethionine (SAM) and acyl-acyl carrier proteins in which the subsequent lactonization causes release of MTA and the acylated homoserine lactone. The acylated homoserine lactone is a bacterial quorum sensing molecule in bacteria that is involved in bacterial virulence against human tissues. Recent work has identified a second communication system (autoinducer 2, AI-2) that is common to both Gram-positive and Gram-negative bacteria and thus has been proposed as a “universal signal” which functions in interspecies cell-to-cell-communication. Again, MTAN generates S-ribosyl-homocysteine (SRH) that is the precursor of AI-2. Inhibition of MTAN or MTAP in microbes will prevent MTA removal and subject the pathway to product inhibition, thereby decreasing production of the quorum sensing pathway and decreasing the virulence of microbial infections. Inhibition of MTAN in microbes will prevent the formation of SRH, decreasing the production of the second quorum sensing pathway.
MTAP deficiency due to a genetic deletion has been reported with many malignancies. The loss of MTAP enzyme function in these cells is known to be due to homozygous deletions on chromosome 9 of the closely linked MTAP and p16/MTS1 tumour suppressor gene. As absence of p16/MTS1 is probably responsible for the tumour, the lack of MTAP activity is a consequence of the genetic deletion and is not causative for the cancer. However, the absence of MTAP alters the purine metabolism in these cells so that they are mainly dependent on the de novo pathway for their supply of purines. That makes these cells unusually sensitive to inhibitors like methotrexate, alanosine and azaserine, that block the de novo pathway. Therefore, a combination therapy of methotrexate, alanosine or azaserine with an MTAP inhibitor will have unusually effective anti-tumour properties.
MTAP inhibitors would also be very effective against parasitic infection such as malaria that infects red blood cells (RBCs), as they lack the de novo pathway for purine biosynthesis. Protozoan parasites depend entirely upon the purines produced by the salvage pathway for their growth and propagation. MTAP inhibitors will therefore kill these parasites without having any negative effect on the host RBCs, as RBCs are terminally differentiated cells and they do not synthesize purines, produce polyamines or multiply.
The imino sugar part of the compounds described most of the patent specifications referred to above has the nitrogen atom located between C-1 and C-4 so as to form 1,4-dideoxy-1,4-imino-D-ribitol compounds. The location of the nitrogen atom in the ribitol ring may be critical for binding to enzymes. In addition, the location of the link between the sugar part and the nucleoside base analogue may be critical for enzyme inhibitory activity. The known compounds have that link at C-1 of the sugar ring.
In the search for new and improved nucleoside phosphorylase and nucleosidase inhibitors, the applicants have Investigated the synthesis and bioactivity of compounds where the location of the nitrogen atom in the sugar ring is varied and, additionally, where two nitrogen atoms form part of the sugar ring. Alternative modes of linking the sugar part and the base analogue have also been investigated.
The applicants have surprisingly found that certain novel compounds exhibit potent inhibitory activity against one or more of PNP, PPRT, MTAP and the nucleoside hydrolase MTAN.
It is therefore an object of the present invention to provide a compound that is an inhibitor of PNP, PPRT, MTAP, MTAN, and/or NH or to at least provide a useful choice.